Titanium IMI 685 BSTOA
Heat-treated state · default condition
BSTOA = beta solution treated (≈1050 °C), oil quenched, aged 550 °C/24 h
Choose this beta solution treated (approx. 1050 °C), oil quenched and 550 °C/24 h aged condition, the standard engine-disc route, for best creep and crack-growth resistance to about 520 °C.
Values for the BSTOA condition
Other IMI 685 tempers and conditions
IMI 685 is listed in 4 conditions; see the grade overview at IMI 685.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As-forged / forging stock (pre heat-treatment) | Disc/ring forging blanks and bar stock supplied for customer-controlled beta heat treatment; properties not certified in this state. | 840 | 950 | 12 | 32 HRC | 1.1 % IACS |
Stress relieved | Applied after heavy machining or welding of BSTOA parts to relieve residual stress without altering the beta-processed microstructure. | 865 | 980 | 11 | 33 HRC | 1.1 % IACS |
BSTOADefaultThis page Beta solution treated (≈1050 °C), oil quenched, aged 550 °C/24 h | Choose this beta solution treated (approx. 1050 °C), oil quenched and 550 °C/24 h aged condition, the standard engine-disc route, for best creep and crack-growth resistance to about 520 °C. | 870 | 990 | 11 | 33 HRC | — |
Α+β annealed | Choose when room-temperature ductility and smooth-specimen fatigue matter more than creep; loses much of the high-temperature advantage. | 900 | 1,000 | 15 | 34 HRC | 1.1 % IACS |
What is IMI 685 BSTOA?
IMI 685 BSTOA is IMI 685 heat treated to BSTOA — choose this beta solution treated (approx. 1050 °C), oil quenched and 550 °C/24 h aged condition, the standard engine-disc route, for best creep and crack-growth resistance to about 520 °C. IMI 685 BSTOA has a yield strength of 870 MPa (126 ksi) and a tensile strength of 990 MPa (144 ksi) — stronger than 76% of titanium grades. Elongation at break is 11% and the elastic modulus is 120 GPa (17.4 Msi). IMI 685 BSTOA has a density of 4.45 g/cm³ (0.161 lb/in³), lighter than 81% of titanium grades. It melts at 1,600°C (2,912 °F).
Advantages
- Stiff — 120 GPa (17.4 Msi), better than 98% of titanium grades
- High service temperature — 520°C (968 °F), better than 97% of titanium grades
- High strength — 870 MPa (126 ksi), better than 76% of titanium grades
Limitations
- Hard to polish — 60/100, worse than 97% of titanium grades
- Difficult to weld — 45/100, worse than 92% of titanium grades
- Limited ductility — 11%, worse than 87% of titanium grades
- Limited formability — 20/100, worse than 83% of titanium grades
IMI 685 BSTOA properties
Typical room-temperature values for IMI 685 BSTOA; 10 are specific to this condition. Other listed values are IMI 685 reference data and may not represent this condition. Bars are the position among titanium grades.
Physical3
IMI 685 BSTOA has a density of 4.45 g/cm³ (0.161 lb/in³), lighter than 81% of titanium grades. It melts at 1,600°C (2,912 °F).
Mechanical15
IMI 685 BSTOA has a yield strength of 870 MPa (126 ksi) and a tensile strength of 990 MPa (144 ksi) — stronger than 76% of titanium grades. Elongation at break is 11% and the elastic modulus is 120 GPa (17.4 Msi).
Thermal6
IMI 685 BSTOA is rated for continuous service to 520°C (968 °F). It conducts heat at 7 W/m·K (4.04 BTU/hr·ft·°F), worse than 76% of titanium grades. Thermal expansion is 9.3 µm/m·K (5.17 µin/in·°F).
Electrical3
IMI 685 BSTOA conducts electricity at 1.1 % IACS, worse than 67% of titanium grades.
Chemical & Environmental3
Corrosion resistance is excellent (86/100), worse than 86% of titanium grades.
Sustainability4
Producing a kilogram of IMI 685 BSTOA takes about 650 MJ of energy and emits 40 kg of CO₂ — less than 75% of titanium grades. Typical recycled content is 15%.
Manufacturability8
IMI 685 BSTOA's machinability is poor (18/100, worse than 83% of titanium grades); weldability fair (45/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with IMI 685 BSTOA
Is IMI 685 easy to machine?
Low speed, high feed, rigid setup, sharp uncoated carbide and flood high-pressure coolant; the Widmanstätten BSTOA structure work-hardens and burns easily, avoid dwell and light rubbing cuts.
Can IMI 685 be welded?
GTAW/EBW in high-purity argon or vacuum with full back purge; weld metal is brittle-prone, so use matching filler, control interstitials and stress relieve at 600–650 °C afterwards.
Can IMI 685 be formed, bent or molded?
Hot work only — forge/roll near or above the beta transus (~1020 °C) with controlled cooling; cold formability is minimal.
What surface finishes work on IMI 685?
Pickle in HNO₃/HF to remove alpha case after hot work; shot peen critical fillets for fatigue, colour anodise for identification, avoid cadmium/silver contact plating.
IMI 685 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Alalpha stabiliser | 5.7 – 6.3 | 6 |
| Zrsolid-solution strengthener | 4.5 – 5.5 | 5 |
| Mobeta stabiliser | 0.4 – 0.6 | 0.5 |
| Sikey creep strengthener (silicide precipitation) | 0.2 – 0.3 | 0.25 |
| Fe | ≤ 0.05 | — |
| Okept low for creep and toughness | ≤ 0.1 | 0.07 |
| C | ≤ 0.04 | — |
| N | ≤ 0.04 | — |
| Hmax, bar/forgings | ≤ 0.01 | — |
| Ti | balance | — |
IMI 685 BSTOA — frequently asked
What is IMI 685 BSTOA used for?
IMI 685 BSTOA is typically used for fan discs, compressor discs, compressor blades, HP compressor drum sections, engine ring and spacer forgings and blade retention hardware. In short: creep-resistant engine disc alloy; 520 °C near-alpha capability; hot-work-only forging grade.
What is the yield strength of IMI 685 BSTOA?
IMI 685 BSTOA has a typical yield strength of 870 MPa (126 ksi) and a tensile strength of 990 MPa (144 ksi) — stronger than 76% of titanium grades. Strength varies by condition: see the 4 listed tempers.
Is IMI 685 BSTOA easy to machine?
Not especially — machinability is rated poor (18/100, worse than 83% of titanium grades). Low speed, high feed, rigid setup, sharp uncoated carbide and flood high-pressure coolant; the Widmanstätten BSTOA structure work-hardens and burns easily, avoid dwell and light rubbing cuts.
Can IMI 685 BSTOA be welded?
With care — weldability is rated fair (45/100). GTAW/EBW in high-purity argon or vacuum with full back purge; weld metal is brittle-prone, so use matching filler, control interstitials and stress relieve at 600–650 °C afterwards.
What surface finishes work on IMI 685 BSTOA?
Pickle in HNO₃/HF to remove alpha case after hot work; shot peen critical fillets for fatigue, colour anodise for identification, avoid cadmium/silver contact plating.
Can IMI 685 BSTOA be formed, bent or molded?
Hot work only — forge/roll near or above the beta transus (~1020 °C) with controlled cooling; cold formability is minimal.
What is the maximum service temperature of IMI 685 BSTOA?
IMI 685 BSTOA is rated for continuous use to about 520°C (968 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between IMI 685 BSTOA and IMI 685 AB-ANN?
BSTOA is the default condition — choose this beta solution treated (approx. 1050 °C), oil quenched and 550 °C/24 h aged condition, the standard engine-disc route, for best creep and crack-growth resistance to about 520 °C. AB-ANN: choose when room-temperature ductility and smooth-specimen fatigue matter more than creep; loses much of the high-temperature advantage. Yield strength is 870 MPa in BSTOA versus 900 MPa in AB-ANN.
Sources
- IMI 685 titanium alloy data sheet — IMI Titanium / Timet UK (1990)
- Materials Properties Handbook: Titanium Alloys — ASM International (1994)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- Titanium: A Technical Guide — ASM International (2000)
- DTD 5153/5163 (IMI 685 bar and forgings) — UK MoD / BSI (1980)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.